How to prevent a user from ssh login (putty)?

Question

SSH

useradd -m -g gameservers -p pass user
How to prevent him from logging in without adding arguments -s /sbin/nologin?
PS: newbie

Answer 1

/etc/default/useradd
....
# Default values ​​for useradd(8)
#
# The SHELL variable specifies the default login shell on your
# system.
# Similar to DHSELL in adduser. However, we use "sh" here because
# useradd is a low level utility and should be as general
# as possible
SHELL=/bin/sh
...

Answer 2

Do not give him a password and check the sshd config for the PermitEmptyPasswords parameter.

Answer 3

Make an entry by key in the OpenSSH server config. Well, in the absence of this, this user simply cannot log in via ssh. Will receive:
Permission denied (publickey).

Answer 4

It can simply make authorization to the server using a certificate via ssh, and not a password.
And to be honest, I don’t understand, do you shine ssh on the entire Internet?
just write in the iptables rules
where ssh is allowed
-A INPUT -p tcp -m state --state NEW -m tcp -s %IP% --dport 22 -j ACCEPT